1. Field Of The Invention
The present invention is concerned with a self-blunting needle assembly especially suited for use as a hypodermic needle, and with hypodermic syringes including such needle assemblies. More particularly, the present invention is concerned with a needle assembly which is self-blunting and disabled after a single use.
2. Description of Related Art
Hypodermic syringes designed to prevent reuse, i.e., designed to be effective for only a single use, are known. For example, U.S. Pat. 4,367,738 discloses a hypodermic syringe in which the plunger rod is fitted with flexible spikes which expand as the plunger is depressed in order to lock the plunger rod within the barrel portion of the syringe, thereby preventing retraction of the plunger rod for reuse of the syringe
U.S. Pat. No. 3,478,937 discloses a syringe in which the plunger stem 23 has a collar unit 25 secured thereon which, when the plunger is pushed through the barrel 11 of the hypodermic syringe, passes through ring 22 mounted at one end of the barrel to prevent subsequent retraction of the plunger for re-use of the device.
U.S. Pat. No. 4,233,975 discloses a syringe in which a plug is positioned in or adjacent to the mouth of the needle so that movement of the plunger rod to expel fluid from the syringe seats a plug which blocks the liquid flow path from the syringe barrel to the needle mouth, thereby disabling the device from further use.
U.S. Pat. No. 4,391,273 discloses a hypodermic syringe in which the plunger carries a protruding pin 67 which punctures a lower wall of the barrel in order to prevent reuse of the hypodermic syringe.
U.S. Pat. No. 1,654,905 discloses a measuring syringe in which a tapering needle 9 has an enlarged head 10 and is mounted for sliding movement within a hollow tube 3, between the positions shown in FIGS. 2 and 3 of the patent. As explained beginning at page 1, line 72 of the patent, the needle 9 acts as a valve to meter a premeasured quantity of liquid into tube 3, and seats with the tip 16 of the needle 9 extending beyond the tip of tube 3 The syringe is then placed against the surface onto which fluid is to be applied and this forces back the tip 16, expelling liquid from the tube 3.
The art also shows syringes which are equipped with means intended to prevent accidental sticking of persons, such as the operator, with the needle. It is estimated that over 2,000 accidental needle-stick wounds are sustained by health care workers in the United States each day. The problem is aggravated by the trend of moving treatment out of hospitals and into doctors' offices and neighborhood clinics as part of a program to reduce health care costs. This trend increases the number and dispersion of health care workers who administer injections and draw blood samples, while reducing the frequency of such injections per individual health care worker. As a consequence, a larger number of less experienced people are administering injections and/or taking blood samples Although in the past an occasional serious illness such as that caused by the hepatitis B virus was sustained as a result of an accidental needle-stick wound, the problem was not considered to be a serious one until the advent of the spreading of human immunodeficiency virus (HIV) infection and the knowledge that this virus is transmissible to health care workers through needle-stick wounds from a contaminated needle. The HIV causes acquired immune deficiency syndrome (AIDS), a disease which, insofar as is presently known, is invariably fatal and which has already killed tens of thousands and infected possibly millions more. HIV is often referred to simply as "the AIDS virus" and the Surgeon General of the United States of America noted in a published (September, 1987) interview that there is no better way to become infected with the AIDS virus than to take blood from an AIDS patient and accidentally inflict a needle-stick wound with the contaminated needle.
This situation has stimulated activity to develop devices which reduce or eliminate the possibility of accidental needle-stick wounds without excessively increasing the unit cost of needles. U.S. Pat. No. 3,890,971 discloses a single use, safety syringe which includes a plunger which is permanently lockable by detent members when the plunger has been operated to expel liquid from the barrel portion of the syringe. The disclosed structure further includes a slidable needle cap which is also permanently lockable by detent members to encase the needle within the sleeve.
Brochures distributed by ICU Medical Inc., of Mission Viejo, Calif., show a hypodermic syringe which has a sheath carried on the needle. Insofar as can be discerned from the brochure, which contains the notation "Patent Pending", the needle extends beyond the sheath for use, and the sheath is grasped by the operator upon withdrawing the needle in order to retract the needle within the sheath upon withdrawal of the needle from the patient In this way, the sheath guards against accidental pricking of the operator with the withdrawn needle.